In various radar systems, several problems are associated with systematic errors in the high-frequency front-end. In particular, a DC offset problem results in a reduction in the performance of a receiver and may thus reduce the detectability of a received signal.
Possible sources of high-frequency impairment in a heterodyne radar system are, in principle, shown in FIG. 1. A scatter signal tL of a first oscillator VC01 may spread to a first mixer 6; moreover, a scatter signal tAnt may be generated by an antenna 14 and by a connection element 13 due to a mismatch. Furthermore, interference signals tR are conceivable due to reflection by a cap element or radome 30 situated in front of antenna 14 and/or due to circuit inaccuracies.
All of the above-named systematic errors may result in a considerable reduction in the performance of the radar sensor, in particular in the case of short range measurements. In order to compensate for these systematic impairments, several studies have already been carried out.
“A fundamental frequency 143-152 GHz radar transceiver with built-in calibration and self-test” CSICS, 2013 describes a heterodyne radar transceiver that includes several self-test and calibration features to make possible a simple production test and a correction of analog front-end impairments.
Patent document DE 10 2009 029 052 A1 discusses a heterodyne radar system in which a reflection signal is formed as an intermediate frequency signal.
“A Digital Leakage Cancellation Scheme for Monostatic FMCW Radar”, IEEE MTT-S Digest, 2004, describes a heterodyne circuitry based on digital real-time signal processing for eliminating leakage effects. Proposed is the generation of a signal having the same amplitude and opposite phase position in relation to the leakage signals to be canceled. However, systematic errors due to antenna or connection mismatch, as well as undesirable reflections in the case of presence of a radome are not considered.
Patent document DE 10 2012 202 007 A1 discusses a radar sensor including an offset compensation unit which generates a compensation signal to be transmitted to the receiver with the received signal.